1. Field of the Invention
This invention relates to an endoscopic treating instrument, more particularly to a coil sheath of an endoscopic treating instrument.
2. Related Art Statement
A conventional treating instrument to be inserted in a forceps channel of an endoscope for making various treatments for internal body tissue comprises, inter alia, a treating portion at the distal end, an operating portion at the proximal end, an operating wire between the operating portion and the treating portion for transmitting the movement of the operating portion to the treating portion at the distal end, and a sheath surrounding the operating wire along its full length.
In order to bend smooth the endoscope in which a treating instrument is inserted, such treating instruments as disclosed in Japanese Laid-Open Patent Applications, Publication Nos. 56-8029 and 59-8946, and Japanese Laid-Open Utility Model Application, Publication No. 53-150092 have been proposed. These prior art publications disclose treating instruments in which the hardness of the sheath is varied in such a manner that the distal end portion is soft so as to be bent and that the other portion is relatively hard.
Further, Japanese Laid-Open Utility Model Application, Publication No. 55-109501 discloses a sheath which comprises a proximal sheath made of a relatively hard coil of a plurality of wires; a distal sheath made of a very flexible coil of a single wire; and a connecting tube connecting the proximal and distal sheaths.
The above-described conventional treating instruments, in which the distal and proximal sheaths having different hardness are connected, have such a drawback as shown in FIG. 1 when they are inserted in a channel of an endoscope. FIG. 1 shows that a treating instrument comprising a soft distal coil sheath 40, a hard coil sheath 41 and a connecting tube 42 connecting both sheaths is broken at the connecting tube 42 where the instrument is weak in rigidity. Consequently, the inner surface of the endoscope channel may be scraped off, and the instrument may be caught in the channel and cannot be drawn out from the endoscope in the worst case.